This invention relates to a linear motor useful for moving and driving movable members of various kinds of machine tools, including laser beam machines.
A recent proposal concerning various kinds of machine tools, including laser beam machines, is to adopt a linear motor for feeding and driving a movable member, such as a machining head, with respect to a workpiece.
When the movable member of a machine tool is moved and driven with a linear motor, substantial heat is generated, such as heat owing to eddy currents generated in a stationary member and a moving member of the linear motor. Joule heating also is generated in the electromagnetic coil(s). This heat can cause thermal deformation of structural or movable members.
The heat is not dissipated uniformly over the whole machine tool. The largest temperature increase typically occurs at the heat generating portion and its vicinity. Heating is less at portions that are far from the heat generating portion. This uneven heating decreases machining efficiency when machining workpieces.
The object of the present invention is to provide a linear motor having good cooling efficiency, taking the above-mentioned circumstances into consideration.
The invention is linear motor having a stationary member and a moving member located so as to face each other. The moving member moves along the stationary member, due to force generated between a magnet and an armature. The linear motor comprises:
a first air flow path for cooling formed along one of the magnet and the armature, located on the stationary member side; and
a first air supply means through which said first air flow path for cooling is supplied with a flow of air.
Provided that the linear motor is effectively cooled so as to minimize temperature differences in the machine tool, machining with high accuracy is possible.
According to an aspect of the invention, said moving member is moved in said first air flow path for cooling.
In this way, both the stationary member and the moving member can be cooled by the flow of air, and machining with even higher accuracy is possible.
According to the invention, a further air flow path for cooling is formed in said moving member so as to communicate with said first air flow path for cooling. The first air flow path for cooling is supplied with air flow by said first air supply means, and part of this air flow proceeds into said further air flow path for cooling so as to cool said magnet or said armature arranged on the moving member.
In this way, the magnet located on the moving member side (or the armature if it is located on the moving member) can be cooled.
In an embodiment of the inventive linear motor, the armature is located on said moving member side, and the magnet is located on said stationary member side.
The armature located on the moving member side or the magnet located on the stationary member side can be cooled.
In another embodiment, the stationary member has a slender shape, the moving member is shaped as a cylinder and fitted on said stationary member with clearance or play to permit movement, the magnets form a magnet row or row of magnetic poles along a longitudinal direction of said stationary member, the armatures form armature rows having two or more rows of armature poles facing said magnet rows, and, said further air flow path for cooling passes between two rows of said armature rows adjacent to each other.
Effective cooling is possible although the linear motor has two or more armature rows, although substantial joule heat may be generated by the multiple armature rows.
A first air supply means can be located on each of two opposite ends of said first air flow path for cooling.
Placing first air supply means on both ends increases the air flow quantity along the first air flow path for cooling.
According to the invention, the linear motor can have a moving member with a coil core, on which an electromagnetic coil is provided, running in a movement area in the shape of a channel formed by or in a stationary member having a magnet row. The coil and the magnet row move and drive a movable member carried on said moving member. The linear motor has a first air flow path for cooling, formed in said movement area. Air streaming along the first air flow path effectively cools the magnet row of the stationary member and the electromagnetic coil and the coil core of the moving member.
A forced air supply means is provided on at least one end of the first air flow path and supplies air for cooling.
Air forced to stream through the first air flow path for cooling removes heat generated at the surface of the stationary member or the moving member of the linear motor.
A second air flow path for cooling can be formed between a supporting member for supporting a magnet row of said stationary member and said magnet row. In that case, a second air supply means for supplying air for cooling said magnet row is provided, in said second air flow path for cooling.
The second air flow path for cooling is also formed between the magnet row of the stationary member of the linear motor and the supporting member supporting this. Air streams along the second air flow path for cooling the stationary member by the second air supply means, providing for more effective cooling of the stationary member.
The first air supply means has at least one of an air blower for intake, provided at one end of said first air flow path, and an air blower for exhaust, provided at the other end of said first air flow path.
Then, air for cooling is forced to stream through the first air flow path by one or both of the air blower for intake or the air blower for exhaust.
According to another aspect, a third air flow path for cooling is formed in a coil core of said moving member so as to penetrate said coil core in its piling direction and so as to stream air for cooling.
The third air flow path is formed in the coil core of the moving member, and cools the moving member.
A pair of guide flow paths can be formed on both sides of said piling direction of said coil core, to communicate each other and to reside in the third air flow path.
In that case, the air for cooling can be streamed through the coil core by the pair of guide flow paths, helping to cool the moving member.
The guide flow path on one side of the piling direction of the coil core preferably communicates with one part of said first air flow path, which is divided by the moving member into a front and a rear part in a moving direction of said moving member. The guide flow path on the other side of the piling direction of the coil core communicates with the other part of said first air flow path for cooling. The front and rear parts of said first air flow path communicate with each other through said guide flow paths and said third air flow path formed in said coil core.
The flow of air in the first air flow path, which path is divided into the front and the rear parts due to the moving member, is substantially unobstructed because the third air flow path traverses the moving member. Effective cooling is possible.
According to further aspects, the linear motor of the invention comprises:
a stationary member having a channel and magnet rows respectively arranged at inner side faces of said channel, facing each other;
a moving member for moving along said magnet rows of said stationary member;
a cover in the shape of a band arranged so as to close over an open portion of said channel of said stationary member; and
a first air flow path for cooling formed by said channel and said cover.
Air along the first air flow path effectively cools the stationary member and the moving member of the linear motor, the first air flow path encompassing the stationary member and the moving member using a simple structure.
A first air supply means supplies forced air to the first air flow path for cooling, such means being provided at either or both ends of said first air flow path.
The forced air streamed along the first air flow path carries along heat generated at the stationary member or the moving member, and the linear motor is effectively cooled.
In one embodiment, a slit is formed in said moving member, extending in a direction of movement of the moving member. The cover extends through the slit on a slider that permits the moving member to slide freely along with the cover passing through the slit.
In this way, the clearance between the stationary member and the cover in the slider is small. The small dimension decreases the volume of air for cooling and the amount that leaks outside, thereby cooling efficiently.
A pair of guide rollers are respectively provided at each of the opposite ends in a direction of movement of the slider. Each guide roller is positioned for guiding the cover, which contacts the guide roller in said slit. Each guide roller contacts and guides the cover up to the opening portion of said stationary member.
This structure defines and confines a small cross section of the air flow path. Thus, the quantity of cooling air that leaks to the outside around the cover is minimal.
The described first air supply means can function also as the described second air supply means. That is, the linear motor can be cooled with a single forced air supply means, making it economical.
The first air supply means preferably has an air blower and an air purifying means for removing foreign objects and purifying the air passing through the blower.
Foreign objects from the outside atmosphere, such as dust and iron powder, are thereby filtered out by the air purifying means. By keeping the inside of the air flow path clean, obstructions owing to foreign objects are prevented. Control of the linear motor is stable. Confidence in operation is improved, and the device is made practical for use in a machine tool plant where foreign objects, such as dust, are routinely present in the air.
In particular, the air purifying means can have a means for removing magnetic metallic powder. This aspect advantageously prevents abrasion of the magnets or the coil cores due to accumulations of magnetic metallic powder. This further improves operations and confidence.
One aspect of the invention is that in the inventive linear motor, the first air supply means as described is provided on the moving member. More particularly, an aspect of the linear motor is that said first air supply means supplies cooling air via an air flow along a path defined through the moving member.